I think these sorts of cases will be very rare, but they will probably work themselves out. As vod said, exclusions can be made for people who are no longer active, but maybe even theymos could step in with the rare cases where someone has died and the issue has been resolved and the feedback can be removed by him if it's silly removing someone just for one feedback, but like I said, it can still be done by current default trust members if the community deems it important enough.
Trust feedback is like when someone is been cursed on whether negative or positive way, it keeps on following them till death. In situation like this, the only person that can undo it, is the person that placed it and nobody else. That's why its always advice to do the right thing at all times to avoid been marked upon negatively
People can be forgiven. DT members are added and removed and that can affect a user positively or negatively.